Room temperature polymerization of acrylate monomers with peroxyesters

ABSTRACT

A composition for preparing polymeric articles comprising: (a) an acrylic polymerizable component such as monomeric and polymeric aliphatic acrylate and methacrylate esters having a Brookfield viscosity of about 0.1-400 poise and about 5-60% by weight of solids; (b) copper and tin polymerization promoters providing in the composition about 0.05-4 ppm of Cu +2  and about 10-300 ppm of Sn +2  ; (c) about 5×10 -6  to 1×10 -4  mole/gm of the composition of a primary mercaptan chain transfer agent; and (d) sufficient peroxyester initiator to provide about 0.02-0.3% by weight of active oxygen in the composition. The composition is highly efficient at room temperature and provides excellent optical quality polymers while permitting a wide choice of peroxyesters as the initiator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the polymerization and curing of acrylic monomers and polymers. More particularly, it relates to the rapid production of acrylic polymers, usually from an acrylic containing syrup, with peroxyester initiators in the presence of a limited group of promoters and chain transfer agents.

2. Description of the Prior Art

U.S. Pat. No. 4,188,315 to Dudinyak is directed to the polymerization of acrylate syrups utilizing formulations which are suitable for room temperature applications, but where good optical properties are not required in the resulting acrylic polymers. Rapid room temperature cures are obtained with the use of metal salts of hemiperesters of maleic acid as the polymerization initiator in the presence of a salt of an oxo acid of sulfur activator.

The article by V. R. Kamath, et al., "Novel Room Temperature Cure System", presented at the 37th Annual Conference, Reinforced Plastics/Composites Institute, The Society of the Plastics Industry, Inc. Session 12-B (Jan. 11-15, 1982), describes a peroxyester initiated room temperature formulation for polyester resins. The system described is not suitable for acrylic systems.

U.S. Pat. No. 3,487,062 to Bodycot describes a system for acrylic polymerization useful at room temperature and providing good optical properties in the acrylic end product. The peroxyester initiator is limited to t-butyl peroxy maleate in combination with stannous chloride, tertiary amine hydrochloride and a mercaptan which are also used in the system.

U.S. Pat. No. 4,189,451 to Dudinyak provides an acrylic polymer at room temperature with a system similar to that of Dudinyak '315.

U.S. Pat. No. 3,775,364 to Duggins describes the polymerization of an acrylic system again utilizing a mercaptan chain transfer agent and a metal salt of a hemiperester such as monotertiary butyl peroxy maleate as a polymerization initiator.

SUMMARY OF THE INVENTION

The present invention describes a composition for preparing polymeric articles suitable for use under ambient conditions if desired and which includes four essential components: (a) a polymerizable component selected from monomeric and polymeric aliphatic acrylics having a Brookfield viscosity of about 0.1-400 poise and about 5-60% by weight of solids; (b) copper and tin polymerization promoters providing in the composition about 0.05-4 ppm of Cu⁺² and about 10-300 ppm of Sn⁺² ; (c) about 5×10⁻⁶ to 1×10⁻⁴ mole/gm of the composition of a primary mercaptan chain transfer agent; and (d) sufficient peroxyester initiator to provide about 0.02-0.3% by weight of active oxygen in the composition.

Where the composition contains all of the above components and the formulation is mixed and cured, an acrylic polymer product of excellent optical quality is obtained at room temperature. The formulation is very efficient in that peak temperatures are reached in a brief period of time, for example on the order of thirty minutes. Exotherms are sufficiently high in the system, resulting in low monomer residue.

A major advantage of the new composition and method is the wide choice of peroxyester initiators permitted. For example, the present compositions may utilize t-buty peroxy benzoate, which has significant advantages from the standpoint of cost as well as stability and relative ease of storage and handling. Also, most of these peroxyesters are available commercially as pure products.

DESCRIPTION OF THE INVENTION

The invention is broadly applicable to the formation of acrylic resins from acrylic monomers and polymers in all of their known variations. Thus, the invention is applicable to monomeric and polymeric aliphatic acrylate and methacrylate esters, both linear and cyclic. The acrylic monomers also include cyanoacrylates as well as the acrylic acids from which the esters are formed.

Usually the starting material to be polymerized will be provided in the form of a "syrup" as that term is understood in this art. A syrup is formed from an acrylic polymer in a liquid acrylic monomer. In general, some polymer content is desired in the syrup so that heat will be retained during the course of the polymerization reaction and thereby accelerate the curing time. The higher viscosity syrups, therefore, provide a more efficient system. The present invention does, however, contemplate the polymerization of acrylic monomers when the monomer is coreacted with ethylene glycol dimethacrylate without the presence of any polymer.

The compositions and methods of this invention are useful for coreacting a curable resin other than an acrylate with the acrylates. Any suitable curable coreactant may be used. In the preferred embodiment, a polyester containing coreactive ethylenic unsaturation is contemplated for coreaction with the selected acrylates.

As indicated, the present invention is advantageous in that it permits employing any one of a broad range of polyester initiators. In the preferred embodiment, the peroxyester is selected from: ##STR1## where R₁ contains up to 13 carbon atoms and is phenyl, alkyl, alkenyl or carboxylic substituted cycloalkyl;

R₂ is t-alkyl of 4-8 carbon atoms; and

R₃ contains up to 13 carbon atoms and is alkyl, alkenyl or carboxylic substituted cycloalkyl. The alkyl and alkenyl groups may be straight or branched chain.

The amounts of the composition to be polymerized are important. The following table summarizes the useful amounts of each component:

    ______________________________________                                         Ingredient                                                                               Useful Range   Optimum Level                                         ______________________________________                                         MMA* Syrup                                                                               0.1-400 poise  >10 poise                                                       5-60% solids   >10% solids                                           Cu.sup.+2 0.05-4 ppm     1-2 ppm                                               Sn.sup.+2 10-300 ppm     100-200 ppm                                           mercaptan 5 × 10.sup.-6 -1 × 10.sup.-4                                                      2.5 × 10.sup.-5 -5 × 10.sup.-5                      mole/gm        mole/gm                                               peroxyester                                                                              0.02-0.3 A.O.**                                                                               >0.07 A.O.                                            ______________________________________                                          *MMA = methyl methacrylate                                                     **A.O. = active oxygen                                                   

With respect to the mercaptan used in the present invention, the only requirement is that it be a primary mercaptan. Particularly satisfactory results have been obtained with laurylmercaptan but any of the other mercaptans described in prior literature could also be utilized. The following work will illustrate the invention.

EXPERIMENTAL Polymerization Runs

All runs were made in 30 ml glass vials (3×6.3 cm) with polyethylene snap caps, and monitored with a type J thermocouple on line to a Rustrak (model 2155A) X-Y potentiometer. A sample size of 10 gms (syrup) was used for all samples and the ingredients were mixed in the vials with a stainless steel spatula.

Promoter Formulations

The 0.005% Cu⁺² and 0.53% Sn⁺² solution was made as follows:

0.75 gms aliquot of 33% SnCl₂.2H₂ O in methanol was added to 24 gms of MMA along with 0.014 gms (1 drop) of copper naphthenate (8%). This mixture was then mixed and stored in an amber bottle. The 0.009% Cu⁺² and 1.05% Sn⁺² solution was made up as described above except 0.03 gms (2 drops) of 8% copper naphthenate and 1.5 gms of 33% SnCl₂.2H₂ O were added to 24 gms of MMA. The other metal solutions were made up in MMA except the iron solutions, which were made up in methanol/MMA (1/5).

Acrylic Syrup

A 3 kg bottle of MMA (Baker) that was autolytically polymerized to 11.5% solids and 50 poise was used for most runs. Other syrups were made from a 40% solids (Elvacite® acrylic resin) in MMA (Baker). All viscosities of resins were determined on a Brookfield Synchro-Lectric viscometer (model HAF).

                  TABLE 1                                                          ______________________________________                                         Peroxides Used in Room Temperature Experiments                                                               %                                                Peroxides          Abbreviation                                                                              Purity  MW                                       ______________________________________                                         1.  di-2-ethylhexyl    2EHP       96.0  346.3                                      peroxydicarbonate                                                          2.  t-butyl perneodecanoate                                                                           TBPN       75.9  244.4                                  3.  t-butylperpivalate TBPP       77.0  174.2                                  4.  diacetyl peroxide  --         18.0  118.1                                  5.  benzoyl peroxide   BPO        98.0  242.2                                  6.  t-butylperoxy 2-ethyl hexanoate                                                                   TBPEH      96.4  216.3                                  7.  t-butylperoxy 2-ethyl hexyl                                                                       TBPEHC     78.5  246.2                                      carbonate                                                                  8.  methylethyl ketone peroxide                                                                       MEKP        9.0%                                                                          A.O.                                         9.  cumene hydroperoxide                                                                              CHP        85.0  146.1                                  10. 1,1-bis(t-butylperoxy)                                                                            11TBPH     98.0  260.4                                      cyclohexane                                                                11. 2,5-dimethyl-2,5-bis(t-butyl                                                                      25TBH      98.0  290.4                                      peroxy) hexane                                                             12. t-butyl peroxybenzoate                                                                            TBPB       98.0  194.2                                  13. 2,5-dimethyl-2,5-bis(2-ethyl                                                                      25TBPEHH   92.0  430.6                                      hexanoyl peroxy)hexane                                                     14. 2,5-dimethyl-2,5-bis(benzoyl                                                                      25TBPBH    78.8  386.4                                      peroxy)hexane                                                              15. t-butylperoxy crotonate                                                                           TBPC       62.3  158.2                                  16. bis-(t-butylperoxy) thio-                                                                         TBPTP      97.0  322.3                                      dipropionate                                                               17. t-amyl peroxy 2-ethylhexanoate                                                                    TAPEH      76.4  230.3                                  18. t-butyl peroxytetrahydro                                                                          TBPTA      91.3  242.3                                      phthalic acid                                                              ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________     Peroxides as Room Temperature Initiators                                       Formulation, parts by weight                                                   MMA syrup (11.5% solids, 50 poise)                                                                           100                                              0.005% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                                                             2                                                0.53% Sn.sup.+2 (1% SnCl.sub.2.2H.sub.2 O in MMA)                                                            2                                                Laurylmercaptan               1                                                Peroxide (used at purity of Table 1)                                                                         2                                                                                Time (hrs)                                                                            Peak                                                                    to Peak                                                                               Exotherm                                Peroxide          % A.O.                                                                              Type     Exotherm                                                                              Temp. (°C.)                      __________________________________________________________________________       diacetyl peroxide                                                                              .048 diacyl peroxide                                                                         gelled                                                                         overnight                                        benzoyl peroxide                                                                               .132 aromatic diacyl                                                                         gelled                                                                peroxide overnight                                        methylethyl ketone                                                                             .180 MEK peroxide                                                                            gelled                                           peroxide                      w/in 48 hrs.                                     cumene hydroperoxide                                                                           .186 hydroperoxide                                                                           gelled                                                                         overnight                                        1,1-bis(t-butyl .241 peroxyketal                                                                             gelled                                           peroxy) cyclohexane           w/in 48 hrs.                                     2,5-dimethyl-2,5-bis                                                                           .216 dialkyl peroxide                                                                        gelled                                           (t-butylperoxy)hexane         w/in 48 hrs.                                     di-2-ethylhexyl .042 peroxy   gelled                                           peroxydicarbonate    dicarbonate                                                                             overnight                                        t-butylperoxy 2-ethyl                                                                          .130 percarbonic                                                                             0.60   110                                       hexyl carbonate      ester                                                     t-butylperoxy 2-ethyl                                                                          .148 peroxy ester                                                                            0.60   120                                       hexanoate                                                                    10.                                                                              t-butylperoxy benzoate                                                                         .161 peroxy ester                                                                            0.40   110                                       t-butylperoxy   .099 peroxy ester                                                                            0.60   102                                       neodecanoate                                                                   t-butylperoxy pivalate                                                                         .142 peroxy ester                                                                            0.35   120                                       2,5-dimethyl-2,5-bis                                                                           .133 diperoxyester                                                                           0.50   105                                       (2-ethylhexanoyl peroxy)hexane                                                 2,5-dimethyl-2,5-bis                                                                           .127 diperoxyester                                                                           0.50   105                                       (benzoyl peroxy)hexane                                                         t-butylperoxy   .126 peroxyester                                                                             0.50   130                                       crotonate                                                                      bis-(t-butylperoxy)                                                                            .194 diperoxyester                                                                           2.25    50                                       thiodipropionate*                                                              t-amyl peroxy   .106 peroxyester                                                                             0.30   130                                       2-ethylhexanoate                                                               t-butyl peroxytetra-                                                                           .121 peroxyester acid                                                                        0.70    80                                       hydrophthalic acid                                                           __________________________________________________________________________      *This system appears to require laurylmercaptan.                         

                  TABLE 3                                                          ______________________________________                                         Effect of Peroxyester Concentration                                            on Cure Rate                                                                   Formulation, parts by weight                                                   MMA syrup (11.5% solids, 50 poise)                                                                       100                                                  0.009% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                                                         1                                                    1.05% Sn.sup.+2 (2% SnCl.sub.2.2H.sub.2 O in MMA)                                                        1                                                    Laurylmercaptan           1                                                                                     Time  Peak                                                            (hrs) to Exo-                                                           Parts           Peak  therm                                                    by              Exo-  Temp.                                   Peroxide         wt.    % A.O.   therm (°C.)                            ______________________________________                                         1.a. t-butyl peroxybenzoate                                                                         0      0      none  none                                  b.   t-butylperoxy 2-ethyl-                                                                         0      0      none  none                                       hexanoate                                                                 2.a. t-butyl peroxybenzoate                                                                         0.5    .040   2.5    65                                   b.   t-butylperoxy 2-ethyl-                                                                         0.5    .036   3.6    50                                        hexanoate                                                                 3.a. t-butyl peroxybenzoate                                                                         1.0    .081   1.0   100                                   b.   t-butylperoxy 2-ethyl-                                                                         1.0    .071   1.0   105                                        hexanoate                                                                 4.a. t-butyl peroxybenzoate                                                                         2.0    .161   0.6   120                                   b.   t-butylperoxy 2-ethyl-                                                                         2.0    .143   0.4   110                                        hexanoate                                                                 5.a. t-butyl peroxybenzoate                                                                         3.0    .242    .7    90                                   b.   t-butylperoxy 2-ethyl-                                                                         3.0    .214    .7   110                                        hexanoate                                                                 ______________________________________                                    

                                      TABLE 4                                      __________________________________________________________________________     Metal Ions as Promoters                                                        Formulation, parts by weight                                                   MMA syrup (11.5% solids, 50 poise)                                                                      100                                                   1.0% SnCl.sub.2.2H.sub.2 O in MMA (0.53% Sn.sup.+2)                                                     1                                                     Laurylmercaptan          0.5                                                   ethylene glycol dimethacrylate                                                                          1                                                     t-butyl peroxybenzoate   2                                                                          Metal                                                                          Ion, Time (hrs)                                                                           Peak                                                            Parts                                                                              Approx.                                                                             to Peak                                                                              Exotherm                                       % Metal Ion                                                                           Type      by wt.                                                                             ppm  Exotherm                                                                             Temp. (°C.)                             __________________________________________________________________________     0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        0        none  none                                           0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        0.1 0.05 4.3   40                                             0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        0.5 0.25 2.5   53                                             0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        1.0 0.5  2.8   58                                             0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        2.0 1    1.6   98                                             0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        3.0 1.5  1.8   98                                             0.005% Cu.sup.+2                                                                      8% Cu Naphthenate                                                                        4.0 2.0  1.7   110                                            0.005% Cu.sup.+2                                                                      Cu(acac)* 1.0 0.5  2.5   65                                             0.005% Co.sup.+2                                                                      Co(acac)  1.0 0.5  none  none                                           0.006% Mn.sup.+2                                                                      Mn(acac)  1.0 0.6  none  none                                           0.003% V.sup.+2                                                                       V(acac)   1.0 0.3  none  none                                           0.005% Ce.sup.+3                                                                      Ce(acac)  1.0 0.5  none  none                                           0.005% Fe.sup.+3                                                                      Fe Cl.sub.3.6H.sub.2 O                                                                   1.0 0.5  gelled                                                                         overnight                                            0.005% Fe.sup.+3                                                                      Fe Cl.sub.3                                                                              2.0 1    gelled                                                                         overnight                                            0.005% Fe.sup.+2                                                                      Fe Cl.sub.2.4H.sub.2 O                                                                   2.0 1    gelled                                                                         overnight                                            __________________________________________________________________________      *acac = acetylacetonate                                                  

                  TABLE 5                                                          ______________________________________                                         Sn.sup.+2 as a Promoter                                                        Formulation, parts by weight                                                   MMA Syrup (11.5% solids, 50 poise)                                                                       100                                                  0.005% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                                                         1                                                    Laurylmercaptan           1                                                    ethylene glycol dimethacrylate                                                                           1                                                    t-butyl peroxybenzoate    2                                                    1% SnCl.sub.2.2H.sub.2 O in MMA (0.53% Sn.sup.+2)                              Parts                Time (hrs)                                                by Weight Conc. Sn.sup.+2                                                                           to Peak   Peak Exotherm                                   0.53% Sn.sup.+2                                                                          Approx. ppm                                                                               Exotherm  Temperature (°C.)                        ______________________________________                                         1.  0          0         none    none                                          2.  0.5        25        3.0     35                                            3.  1.0        50        2.2     70                                            4.  2.0       100        1.0     95                                            5.  3.0       150         .8     95                                            6.  4.0       200         .9     70                                            7.  6.0       300         .9     60                                            ______________________________________                                    

                  TABLE 6                                                          ______________________________________                                         Mercaptan as Promoter/Chain Transfer Agent                                     Formulation, parts by weight                                                   MMA syrup (11.5% solids, 50 poise)                                                                       100                                                  0.005% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                                                         1                                                    1.0% SnCl.sub.2.2H.sub.2 O in MMA (0.53% Sn.sup.+2)                                                      1                                                    t-butyl peroxybenzoate    2                                                    ethylene glycol dimethacrylate                                                                           1                                                                                       Peak                                                                 Time      Exotherm                                                     Parts   (hrs.) to Temp.                                       Mercaptan        by wt.  Exotherm  (°C.)                                ______________________________________                                         Laurylmercaptan  0       none      none                                        Laurylmercaptan  0.1     2.4       50                                          Laurylmercaptan  0.5     2.8       58                                          Laurylmercaptan  1.0     2.2       70                                          Laurylmercaptan  2.0     2.0       50                                          Lauryl-3-mercapto propionate                                                                    0.5     2.0       70                                          2-mercapto ethanol                                                                              0.5     2.5       55                                          2-mercapto benzothiozole                                                                        0.6     none      none                                        ______________________________________                                    

                  TABLE 7                                                          ______________________________________                                         Effect of Syrup Viscosity and % Solids                                         on the Cure Rate                                                               Formulation, parts by weight                                                   MMA syrup                 100                                                  0.009% Cu.sup.+2 (from 8% Cu.Naphthenate in MMA)                                                         1                                                    1.05% Sn.sup.+2 (2% SnCl.sub.2.2H.sub.2 O in MMA)                                                        1                                                    Laurylmercaptan           1                                                    Syrup              Time (hrs.) Peak Exotherm                                   % Solids  Viscosity                                                                               Peak Exotherm                                                                              Temperature (°C.)                        ______________________________________                                         1.   40*      300 poise                                                                               0.3       100                                           2.   30*      9.2 poise                                                                               0.5       100                                           3.   20*      0.13 poise                                                                              1.8        70                                           4.   11.5     50 poise 0.6       120                                           ______________________________________                                          *DuPont, Elvacite ® acrylic resin (grade 2010)                       

                  TABLE 8                                                          ______________________________________                                         Effect of Different Monomers                                                   on the Cure Rate                                                               Formulation, parts by weight                                                   Monomer or syrup          100                                                  0.009% Cu.sup.+2 (from 8% Cu.Naphthanate in MMA)                                                         1                                                    1.05% Sn.sup.+2 (2% SnCl.sub.2.2H.sub.2 O in MMA)                                                        1                                                    Laurylmercaptan           1                                                    t-butyl peroxybenzoate    2                                                                                 Time    Peak                                                                   (hrs) to                                                                               Exo-                                                                   Peak    therm                                                        % Solids  Exo-    Temp.                                     Monomer            as PMMA*  therm   (°C.)                              ______________________________________                                         1.  ethylacrylate      30        0.06  200                                     2.  ethylacrylate      0         0.10  200                                     3.  ethylene glycol    0         0.05  200                                         dimethacrylate                                                             4.  allyl diglycol carbonate                                                                          0         no rxn.                                                                              --                                      5.  allyl diglycol carbonate/                                                                         0         0.06  200                                         ethylene glycol dimethacrylate                                                 (50:50)                                                                    6.  allyl diglycol carbonate/                                                                         0         0.3**  38                                         ethylene glycol dimethacrylate                                                 (90:10)                                                                    7.  styrene            0         no rxn.                                                                              --                                      8.  MMA/ethylene glycol                                                                               0         1.25  130                                         dimethacrylate (90:10)                                                     9.  styrene/ethylene glycol                                                                           0         no rxn.                                                                              --                                          dimethacrylate (80:20)                                                     10. methacrylic acid   0         0.05  200                                     11. general purpose orthophthalic                                                                     NA        0.08  150                                         unsaturated polyester resin/                                                   ethylene glycol dimethacrylate                                                 (85:15)                                                                    12. acrylonitrile      0         0.08  120                                     13. MMA/acrylonitrile (75/25)                                                                         12        0.10  100                                     ______________________________________                                          *DuPont, Elvacite ® acrylic resin (grade 2010)                             **Resulted in a hazy gell which became clear after post curing.           

I claim:
 1. A composition useful for preparing polymeric articles at ambient temperature and pressure comprising:(a) a polymerizable component selected from monomeric and polymeric aliphatic acrylics substantially free of ethylene monomer having a Brookfield viscosity of about 0.1-400 poise and about 5-60% by weight of solids; (b) copper and tin polymerization promoters providing in the composition about 0.05-4 ppm of Cu⁺² and about 10-330 ppm of Sn⁺² ; (c) about 5×10⁻⁶ to 1×10⁻⁴ mole/gm of the composition of a primary mercaptan chain transfer agent; and (d) sufficient peroxyester initiator to provide about 0.02-0.3% by weight of active oxygen in the composition.
 2. A composition in accordance with claim 1 wherein said peroxyester initiator is selected from the formulas: ##STR2## where R₁ contains up to 13 carbon atoms and is phenyl, alkyl, alkenyl or carboxylic substituted cycloalkyl;R₂ is t-alkyl of 4-8 carbon atoms; and R₃ contains up to 13 carbon atoms and is alkyl, alkenyl or carboxylic substituted cycloalkyl.
 3. A composition in accordance with claim 1 wherein said polymerizable component (a) is a syrup comprising a polymer and a monomer.
 4. A composition in accordance with claim 1 wherein said polymerizable component (a) comprises a monomer and ethylene glycol dimethacrylate.
 5. A composition in accordance with claim 1 wherein said polymerizable component (a) contains a curable coreactant for said acrylics.
 6. A composition in accordance with claim 5 wherein said coreactant is a polyester containing co-reactive ethylenic unsaturation.
 7. A composition in accordance with claim 1 wherein said polymerizable component (a) has a viscosity of at least about 10 poise and is at least about 10% by weight of solids; said copper and tin promoters (b) provide at least about 1-2 ppm of Cu⁺² and 100-200 ppm of Sn⁺² ; said mercaptan chain transfer agent (c) comprises about 2.5×10⁻⁵ to 5.0×10⁻⁵ mole/gm of the composition; and said peroxyester initiator (d) provides at least about 0.07% by weight of active oxygen in the composition.
 8. A composition in accordance with claim 1 wherein said peroxyester is selected from t-butyl peroxy 2-ethyl hexyl carbonate, t-butyl peroxy 2-ethyl hexanoate, t-butyl peroxy neodecanoate, t-butyl peroxy pivalate, 2,5-dimethyl-2,5-bis(2-ethylhexanoyl peroxy)hexane, 2,5-dimethyl-2,5-bis(benzoyl peroxy)hexane, t-butyl peroxy crotonate, bis-(t-butyl peroxy) thiodipropionate, t-amyl peroxy 2-ethylhexanoate and t-butyl peroxytetrahydrophthalic acid.
 9. A composition in accordance with claim 1 wherein the peroxyester is t-butyl peroxybenzoate.
 10. A composition in accordance with claim 1 wherein said mercaptan chain transfer agent (c) is selected from lauryl-mercaptan, lauryl-3-mercapto propionate and 2-mercapto ethanol.
 11. A process for making acrylic polymers comprising: mixing the composition of claim 1 and curing the same under ambient conditions.
 12. A process for making acrylic polymers comprising: mixing the composition of claim 2 and curing the same under ambient conditions.
 13. A process for making acrylic polymers comprising: mixing the composition of claim 3 and curing the same under ambient conditions.
 14. A process for making acrylic polymers comprising: mixing the composition of claim 4 and curing the same under ambient conditions.
 15. A process for making acrylic polymers comprising: mixing the composition of claim 5 and curing the same under ambient conditions.
 16. A process for making acrylic polymers comprising: mixing the composition of claim 6 and curing the same under ambient conditions.
 17. A process for making acrylic polymers comprising: mixing the composition of claim 7 and curing the same under ambient conditions.
 18. A process for making acrylic polymers comprising: mixing the composition of claim 8 and curing the same under ambient conditions.
 19. A process for making acrylic polymers comprising: mixing the composition of claim 9 and curing the same under ambient conditions.
 20. A process for making acrylic polymers comprising: mixing the composition of claim 10 and curing the same under ambient conditions. 